Because of the high reliance of XML files, I am having a very hard time figuring out the cause of this error when creating a custom admin grid:

Fatal error: Method Magento\Ui\TemplateEngine\Xhtml\Result::__toString() must not throw an exception in C:\wamp64\www\mage2\vendor\magento\module-ui\Component\Wrapper\UiComponent.php on line 0

I am trying to make an admin grid for the sales_shipment_item table.

So far I have:

1. Used xdebug and put it within the __toString() method of the Result class, it does not show what the real error is

2. I have var_dumped the variables within the __toString() method

3. I have developer mode turned on in Magento 2

4. I have checked the var/logs and it shows nothing helpful

I have successfully made other admin custom grids, but trying to figure out the actual error is like a needle in a haystack. Has anyone found a better way of debugging these? I have looked over all the grid xml, di.xml, and models and all looks ok.